1. Field of the Invention
The present invention relates to a projection display apparatus with colored light combining means and a lighting optical system therefor.
2. Discussion of the Background
A cross dichroic prism is often used for projection display apparatus that project a color image on a projection screen. For example, in a transmissive liquid-crystal projector, the cross dichroic prism is utilized as colored light combining means that combines three colored rays of red, green, and blue and emits the composite light in a common direction. In a reflective liquid-crystal projector, the cross dichroic prism is utilized as colored light separation means that separated a beam of white light into three colored rays of red, green, and blue and also as colored light combining means that recombines modulated three colored rays and emits the composite light in a common direction. A known example of the projection display apparatus with the cross dichroic prism is disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 1-302385.
FIG. 17 conceptually illustrates a main part of a projection display apparatus. The projection display apparatus includes three liquid-crystal light valves 42, 44, and 46, a cross dichroic prism 48, and a projection lens system 50. The cross dichroic prism 48 combines three colored rays of red, green, and blue modulated by the three liquid-crystal light valves 42, 44, and 46 light and emits the composite light toward the projection lens system 50. The projection lens system 50 focuses the composite light on a projection screen 52.
FIG. 18 is a partly decomposed perspective view illustrating the cross dichroic prism 48. The cross dichroic prism 48 includes four right-angle prisms which are bonded to one another via the respective right-angle surfaces by an optical adhesive.
FIG. 19 shows a problem arising in the case of utilizing the cross dichroic prism 48. As shown in FIG. 19(A), the cross dichroic prism 48 has a red light reflection film 60R and a blue light reflection film 60B which are arranged in a substantially X shape on an X-shaped interface formed by the right-angle surfaces of the four right-angle prisms. There is an X-shaped layer of optical adhesive 62 formed in the gaps between the four right-angle prisms. Both the reflection films 60R and 60B accordingly have gaps at a central axis 48a of the cross dichroic prism 48.
When a light beam passing through the central axis 48a of the cross dichroic prism 48 is projected on the projection screen 52, a dark line due to the central axis 48a may be formed in the projected image. FIG. 19(B) shows an example of the dark line DL. The dark line DL represents a relatively dark, linear area having a different color from that of the other part and is formed substantially on the center of the projected image. It is considered that the dark line DL is ascribed to scattering of rays and no-reflection of the red light and blue light in the gaps of the reflection films in the vicinity of the central axis 48a. A similar problem arises in a cross dichroic mirror that includes two dichroic mirrors that are arranged in an X shape and respectively have selective reflection films, such as a red reflection film and a blue reflection film. In this case, a dark line due to a central axis of the mirror is formed in a projected image.
As described above, in the prior-art projection display apparatus, a dark line is formed substantially on the center of a projected image because of the central axis of the cross dichroic prism 48 or the cross dichroic mirror.
The object of the present invention is thus to solve the above problem in the prior art and make a dark line due to a central axis of an optical means inconspicuous, where the optical means includes two dichroic films arranged substantially in an X shape and may be a cross dichroic prism or a cross dichroic mirror.
The principle for solving the problem is described first with a concrete example shown in FIGS. 1 through 4. In the drawings, z direction denotes the direction of the course of light, x direction denotes the direction of 3 o""clock seen from the direction of the course of light (the z direction), and y direction denotes the direction of 12 o""clock. In the description below, the x direction represents the direction of rows and the y direction represents the direction of columns for the matter of convenience. Although the description of the principle is based on a concrete example for the better understanding, the present invention is not restricted to this concrete structure in any sense.
In a projection display apparatus, a lighting optical system with two lens arrays each including a plurality of small lenses (hereinafter referred to as an integrator optical system) as specified in WO94/22042 is known as the technique for dividing light from a light source into a plurality of partial light fluxes and thereby reducing an in-plane unevenness of the illuminance of light.
FIG. 1 shows the principle of forming a dark line when an integrator optical system is adopted in a projection display apparatus with a cross dichroic prism. FIGS. 1(A-1) and 1(B-1) show light fluxes (shown by the solid lines) passing through a plurality of small lenses 10 which are different in position in the x direction, that is, a plurality of small lenses 10 existing in different columns, and traces of their central optical axes (shown by the fine dotted lines). FIGS. 1(A-2) and 1(B-2) show the positions of dark lines DLa and DLb formed on a screen 7.
A light flux emitted from a light source (not shown) is divided into a plurality of partial light fluxes by first and second lens arrays 1 and 2 each including the plurality of small lenses 10. The light fluxes passing through the respective small lenses 10 included in the first and the second lens arrays 1 and 2 are converted to light fluxes parallel to the respective central axes of the partial light fluxes by means of a paralleling lens 15. The partial light fluxes passing through the paralleling lens 15 are superposed on a liquid-crystal light valve 3, so that a predetermined area is uniformly illuminated with the superposed light fluxes. Although only one liquid-crystal light valve 3 is shown in FIG. 1, the principle of the integrator optical stem and the principle of forming a dark line are also applicable to the her two liquid-crystal light valves.
FIG. 2 is a perspective view illustrating the appearance of the first and the second lens arrays 1 and 2. Each of the first and the second lens arrays 1 and 2 includes the small lenses 10 that respectively have a substantially rectangular outline and are arranged in a matrix of M rows and N columns. In this example, M=10 and N=8. FIG. 1(A-1) shows the trace of partial light fluxes passing through the small lenses 10 of the second column, whereas FIG. 1(B-1) shows the trace of partial light fluxes passing through the small lenses 10 of the seventh column.
The light fluxes superposed on the liquid-crystal light valve 3 are subjected to modulation responsive to image information in the liquid-crystal light valve 3 and enter a cross dichroic prism 4. The light flux output from the cross dichroic prism 4 is projected on the screen 7 via a projection lens system 6.
As shown by the rough dotted lines in FIGS. 1(A-1) and 1(B-1), light fluxes passing through a central axis 5 (along the y direction in the drawing) of the cross dichroic prism 4 are projected at positions Pa and Pb on the screen 7. As discussed previously in the prior art, scattering of the rays and no-reflection of the light to be reflected in the gaps between reflection films in the vicinity of the central axis 5 reduce the quantity of light passing through the vicinity of the central axis 5. As shown in FIGS. 1(A-2) and 1(B2), the reduction causes dark lines DLa and DLb, which have the lower luminance than the area around luminance on the projection screen 7.
The dark line has the following relation to the first and the second lens arrays 1 and 2. As clearly shown in FIG. 3(A), which is a partial enlarged view of FIG. 1(A-1), the image formed by the liquid-crystal light valve 3 is inverted and magnified by the projection lens system 6 and projected on the projection screen 7. FIG. 3(B) is a cross sectional view showing an x-y plane including the central axis 5 of the cross dichroic prism 4. Referring to FIGS. 3(A) and 3(B), in case that a partial light flux is cut by the x-y plane including the central axis 5 of the cross dichroic prism 4, r1 denotes a distance from one end 11 of a cross section 8 of the partial light flux to the central axis 5, and r2 denotes a distance from the other end 12 of the cross section 8 of the partial light flux to the central axis 5. The image of the cross section 8 of the partial light flux is inverted and magnified by the projection lens system 6 and projected on the projection screen 7. A ratio of a distance R2 from one end 13 of a projection area 9 on the projection screen 7 to the dark line DLa to a distance R1 from the other end of the projection area 9 to the dark line DLa is accordingly equal to the ratio of r2 to r1. In other words, the position where the dark line DLa is formed depends upon the position where the cross section 8 of the partial light flux exists relative to the central axis 5 in the x-y plane including the central axis 5 of the cross dichroic prism 4.
In the examples of FIGS. 1(A-1) and 1(B-1), the partial light fluxes have cross sections at different positions in the x-y plane including the central axis of the cross dichroic prism 4. This means that the dark lines DLa and DLb are formed at different positions. In a similar manner, the partial light fluxes passing through the small lenses 10 existing in the columns other than the second column and the seventh column in the first and the second lens arrays 1 and 2 have cross sections at different positions in the x-y plane including the central axis 5 of the cross dichroic prism 4. A number of dark lines corresponding to the number of columns included in the first and the second lens arrays 1 and 2, N dark lines in this example, are thus formed on the projection screen 7.
The partial light fluxes passing through the M small lenses arranged on the same column in the first and the second lens arrays 1 and 2 form dark lines DLc at approximately the same position on the projection screen 7 as shown in FIG. 4. Each of the N dark lines is formed by superposing the partial light fluxes passing through the M small lenses arranged on the same column in the first and the second lens arrays 1 and 2. The degree of darkness of each dark line is substantially identical with the summation of the degree of darkness of the dark lines formed by the respective small lenses.
The above description leads to the following principles.
(First Principle)
The first principle is that the different positions of the central axes of the partial light fluxes relative to the central axis 5 of the cross dichroic prism 4 cause dark lines to be formed at different positions. The partial light fluxes passing through the different columns included in the first and the second lens arrays 1 and 2 are different in position relative to the central axis 5 of the cross dichroic prism 4 and thereby form dark lines at different positions.
(Second Principle)
The second principle is that the different positions of the cross sections of the partial light fluxes in the x-y plane including the central axis 5 of the cross dichroic prism 4 are ascribed to the difference in incident angles of the partial light fluxes entering the cross dichroic prism 4 (see FIG. 1). The partial light fluxes passing through the different columns included in the first and the second lens arrays 1 and 2 enter the cross dichroic prism 4 at different incident angles and thereby have cross sections at different positions relative to the central axis 5.
Namely different incident angles of the partial light fluxes entering the cross dichroic prism 4 or different angles of the partial light fluxes superposed on the liquid-crystal light valve 3 cause dark lines to be formed at different positions.
(Conclusions)
As discussed previously, the partial light fluxes passing through the M small lenses arranged on the same column in the first and the second lens arrays 1 and 2 respectively form dark lines at substantially the same position on the projection screen 7. The degree of darkness of each resulting dark line is substantially equal to the summation of the degree of darkness of the dark lines formed by the respective small lenses. A desired arrangement accordingly causes dark lines to be formed at different positions on the projection screen 7 by the respective partial light fluxes passing through the M small lenses. Although increasing the total number of dark lines, this arrangement decreases the degree of darkness per each dark line, thereby making each dark line sufficiently inconspicuous. It is, however, not required to cause all the dark lines to be formed at different positions by the respective partial light fluxes passing through the M small lenses. One preferable application accordingly causes only part of the dark lines to be formed at different positions.
Formation of dark lines at different positions is realized according to either one of the first principle and the second principle discussed above.
Based on the first principle, as for part of the partial light fluxes passing through the M small lenses arranged on the same column, the positions of the central axes of the partial light fluxes relative to the central axis 5 of the cross dichroic prism 4 should be changed from the others.
Based on the second principle, as for part of the partial light fluxes passing through the M small lenses arranged on the same column, the angles of the partial light fluxes superposed on the liquid-crystal light valve 3 or the incident angles of the partial light fluxes entering the cross dichroic prism 4 should be changed from the others.
The present invention has solved the problem of the prior art discussed previously according to the above principles. The following describes the means for solving the problem and its functions and effects.
(Means for Solving Problems and its Functions and Effects)
The present invention is directed to a lighting optical system for emitting light for use in a projection display apparatus comprising: colored light separation means which separates the light into three colored rays; three light modulation means which respectively modulate the three colored rays based on given image signals; colored light combining means which has two dichroic films arranged in an X shape and a central axis corresponding to a position where the two dichroic films cross each other, the colored light combining means combining the three colored rays respectively modulated by the three light modulation means to composite light and outputting the composite light in a common direction; and projection means which projects the composite light output from the colored light combining means on a projection surface, the lighting optical system comprising: a dividing and superposing optical system that divides a light flux into a plurality of partial light fluxes, which are arranged in directions of columns and rows, and superposes the plurality of partial light fluxes, the columns being substantially parallel to the central axis of the colored light combining means, the rows being substantially perpendicular to the direction of columns, wherein the dividing and superposing optical system is constructed to shift, in the direction of rows, an illumination area on each light modulation means illuminated with part of the partial light fluxes among the partial light fluxes on an identical column from an illumination area illuminated with the other partial light fluxes among the partial light fluxes on the identical column.
One partial light flux projects the central axis of the colored light combining means on the projection surface and forms a dark line corresponding to the central axis. A plurality of partial light fluxes arranged on one column generally project the central axis of the colored light combining means at substantially the same position on the projection surface and forms a dark line. In the above arrangement, the illumination area on the light modulation means illuminated with part of the partial light fluxes is shifted from the illumination area illuminated with the other partial light fluxes in the direction of rows (in the direction virtually perpendicular to the direction of columns substantially parallel to the central axis). Based on the first principle discussed above, the position of the central optical paths of the part of the partial light fluxes relative to the central axis of the colored light combining means can be shifted from the position of the central optical paths of the other partial light fluxes. This causes the part of the partial light fluxes and the other partial light fluxes to form dark lines at different positions. This arrangement accordingly makes the dark lines formed on a projected image sufficiently inconspicuous.
In accordance with one preferable arrangement of the lighting optical system, the dividing and superposing optical system comprises: a first lens array having a plurality of small lenses arranged in the directions of columns and rows; and a second lens array having a plurality of small lenses respectively arranged corresponding to the plurality of small lenses of the first lens array, wherein, in the second lens array, at least part of the small lenses among at least one column of the small lenses arranged in the direction of columns have optical centers different from optical centers of the other small lenses in the at least one column.
In this preferable arrangement, among a plurality of small lenses arranged at least on one column, part of the small lenses, which part of the partial light fluxes pass through, have optical centers at a different position from optical centers of the other small lenses. This causes the optical paths of the part of the partial light fluxes to be shifted from the optical paths of the other partial light fluxes. Based on the first principle discussed above, this arrangement prevents the plurality of partial light fluxes from projecting the central axis of the colored light combining means at substantially the same position. This accordingly makes dark lines formed on a projected image sufficiently inconspicuous.
In the lighting optical system of this arrangement, it is preferable that the part of the small lenses are eccentric lenses having optical centers at a different position from the position of the optical centers of the other small lenses, in order to cause an illumination area on a lighting area by the partial light fluxes passing through the part of the small lenses to be shifted in the direction of rows from an illumination area on the lighting area by the partial light fluxes passing through the other small lenses.
This arrangement causes the optical paths of the partial light fluxes passing through the part of the small lenses to be shifted from the optical paths of the partial light fluxes passing through the other small lenses. Based on the first principle discussed above, this arrangement prevents the plurality of partial light fluxes from projecting the central axis of the colored light combining means at substantially the same position. This accordingly makes dark lines formed on a projected image sufficiently inconspicuous.
In the lighting optical system of the above arrangement, it is preferable that a plurality of small lenses located on an identical column are divided into a plurality of groups, small lenses included in an identical group have optical centers at an identical position relative to a lens center, and small lenses included in different groups have optical centers at different positions relative to the lens center.
In this arrangement, the respective groups have different optical paths of the partial light fluxes passing through the small lenses. Namely the respective groups form the dark line corresponding to the projected central axis of the colored light combining means at different positions and prevents the central axis of the colored light combining means from being projected at substantially the same position.
It is further preferable that the plurality of small lenses located on an identical column are divided into the plurality of groups so that a total quantity of light of the partial light fluxes passing through each of the plurality of groups is equal to each other.
The difference in total quantity of light of the partial light fluxes passing through each group varies the degree of darkness of the dark line corresponding to the central axis of the colored light combining means projected by the partial light fluxes passing through the group. The object of the present invention is to make these dark lines sufficiently inconspicuous. The human""s eyes have relatively high discriminating power based on the relative comparison, and the difference in degree of darkness among the dark lines is accordingly undesirable. The identical total quantity of light of the partial light fluxes passing through each group thus equalizes the degree of darkness of the dark lines formed by the partial light fluxes passing through the respective groups.
The plurality of groups may be at least two sections divided in the direction of columns. This simple arrangement prevents the central axis of the colored light combining means from being projected at substantially the same position.
In one preferable arrangement, the plurality of groups are two sections divided in the direction of columns, optical centers of a plurality of small lenses included in one of the two sections and optical centers of a plurality of small lenses included in the other of the two sections are symmetrical about the lens center.
In this arrangement, the other section includes the same small lenses as those of one section, which are arranged upside down. Namely the second lens array consists of only one type of small lenses.
In the lighting optical system of any one of the above arrangement, it is preferable that the plurality of small lenses included in the second lens array have optical centers that are arranged symmetrically about a center of the second lens array corresponding to a center of an optical axis of a light source.
The light source used in the projection display apparatus generally has the largest quantity of light on the center of the optical axis, and the quantity of light decreases with an increase in distance from the center of the optical axis. In case that such a light source is used in the projection display apparatus, the above preferable arrangement can equalize the degree of darkness of all the plurality of dark lines corresponding to the central axis of the colored light combining means projected by the partial light fluxes passing through the plurality of small lenses included in the second lens array.
In the lighting optical system of any one of the above arrangement, in accordance with one application, the dividing and superposing optical system further comprises: a superposing lens which superposes and condenses a plurality of partial light fluxes, which have passed through the plurality of small lenses in the first lens array and the plurality of small lenses in the second lens array, substantially on an illuminating position of each light modulation means; and a polarizing element interposed between the second lens array and the superposing lens, wherein the polarizing element comprises: a polarization beam splitter array which has plural sets of a polarization separating film and a reflecting film that are parallel to each other, the polarization beam splitter array separating each of the plurality of partial light fluxes passing through the plurality of small lenses of the second lens array into two types of linear polarized light components; and a polarizer which equalizes polarizing directions of the two types of linear polarized light components separated by the polarization beam splitter array.
This arrangement converts the light including rays of random polarized light to one type of polarized light and thereby enhances the utilization efficiency of light.
The present invention is also directed to a projection display apparatus comprising: a lighting optical system which emits light; colored light separation means which separates the light into three colored rays; three light modulation means which respectively modulate the three colored rays based on given image signals; colored light combining means which has two dichroic films arranged in an X shape and a central axis corresponding to a position where the two dichroic films cross each other, the colored light combining means combining the three colored rays respectively modulated by the three light modulation means to composite light and outputting the composite light in a common direction; and projection means which projects the composite light output from the colored light combining means on a projection surface, wherein the lighting optical system comprises a dividing and superposing optical system that divides a light flux into a plurality of partial light fluxes, which are arranged in directions of columns and rows, and superposes the plurality of partial light fluxes, the columns being substantially parallel to the central axis of the colored light combining means, the rows being substantially perpendicular to the direction of columns, and wherein the dividing and superposing optical system is constructed to shift, in the direction of rows, an illumination area on each light modulation means illuminated with part of the partial light fluxes among the partial light fluxes located on a same column from an illumination area illuminated with the other partial light fluxes among the partial light fluxes located on the identical column.
Like the respective lighting optical systems described above, the projection display apparatus including any one of the above lighting optical systems can make dark lines formed on a projected image sufficiently inconspicuous.